Leadframe having selective planishing

Abstract

A metal leadframe strip (500) for semiconductor devices is described. The leadframe strip has a plurality of sites (510) for assembling semiconductor chips. The sites alternate with zones (520) for connecting the leadframe to molding compound runners. The sites (510) have mechanically rough and optically matte surfaces (511, 512). The zones (520) have at least portions with mechanically flattened and optically shiny metal surfaces (521, 522). The flattened surface portions transition into the rough surface portions by a step.

Description

FIELD OF THE INVENTION[0001]The present invention is related in general to the field of semiconductor devices and processes, and more specifically to the structure and fabrication process of flood-plated rough metallic leadframes in semiconductor packages having selectively planished portions to reduce the leadframe adhesion to molding compound in zones exposed to compound in mold runners.DESCRIPTION OF RELATED ART[0002]Based on their functions, semiconductor packages include a variety of different materials. Metals formed as leadframes and bonds are employed for mechanical stability and electrical and thermal conductance, and insulators, such as polymeric molding compounds, are used for encapsulations and form factors. In the packaging fabrication flow, it is common practice to attach a plurality of semiconductor chips to a strip of leadframe, to connect the chips to their respective leads, and then to encapsulate the assembled chips in packages, which protect the enclosed parts ag...

AI Technical Summary

Benefits of technology

[0009]Among dominating market trends for semiconductor products are the demand for increased insensitivity against temperature variations and moisture level exposure, and the need to keep fabrication cost down by employing inexpensive process steps. For semiconductor packages, the first trend implies an increased need for creating reliable adhesion between the different package parts and maintaining the adhesion through mechanically rough process steps, such as degating, deflashing, and trimming and forming. The second trend implies a necessity to avoid expensive process techniques such as selective plating and to select inexpensive process steps throughout such as flood plating.

[0012]In a careful failure analysis, applicant discovered as the root cause of the leadframe deformation the enhanced adhesion between the roughened leadframe surfaces and the molding compound in zones such as the mold runners where the plastic crosses the leadframe strip outside the package.

Problems solved by technology

In addition, the requirement to use lead-free solders pushes the reflow temperature range into the neighborhood of about 260° C., making it more difficult to maintain mold compound adhesion to the leadframes.

Analyzing quality and productivity issues of molded plastic devices, applicant observed that the process steps of degating after molding frequently causes deformation of the leadframe during the gate removal step.

As a consequence of this deformation, yield losses of approximately 5% may occur at the process step of trimming-and-forming.

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